HOM/HOX genes play an important role in body plan formation of insects and vertebrates. Hydra is one of the classic objects for investigation of pattern formation mechanisms. The pattern forming processes of this animal are well understood. The overall question is what is the role the HOM/HOX genes in pattern formation of hydra. Cnox genes of HOM/HOX class were recently described for hydra. Once their role is understood one would (1) enhance the understanding of the pattern forming processes at the molecular level in hydra, (2)strengthen the evidence for the early appearance in metazoan evolution of common developmental mechanisms among animals, and (3) provide further refinements for the understanding of the role of this class of genes. Six Cnox genes have been identified in hydra. The aim of this proposal is to characterize one of them, Cnox-4. The gene will be isolated, sequenced, and compared with known HOM/HOX genes. An antibody will be generated against the protein product of the gene. The antibody will be used to determine the expression pattern of the gene in normal animals which will suggest its role in patterning processes. Then the Cnox-4 expression pattern will be examined in a variety of situations in which the pattern forming processes are altered. This occurs in mutants, and in operated animals with graftings. The nature of the changes in expression patterns will probably indicate the role of Cnox-4 in the patterning events of hydra. The linkage with other Cnox genes will be examined to determine if the unusual linkage of HOM/HOX genes found in vertebrates and insects also occurs in hydra which would also indicate the early evolution of this arrangement.